Important Facts for Earthquakes

Definition

Earthquakes are among the most devastating of all the earth's natural disasters and can result in high death rates, mass casualties, or traumatic injuries.

Numerator

Number of earthquakes by magnitude category

Denominator

Denominator, if needed, is based on county characteristics. One denominator for the earthquake indicators is the number of people in the county and the other is the number of square miles in the county.

Why Is This Important?

Earthquakes are defined as the shaking of the earth caused by waves moving on and below the earth's surface causing: surface faulting, tremors, vibration, liquefaction, landslides, aftershocks and/or tsunamis. Earthquakes have caused over 780,000 deaths in the past decade alone, accounting for nearly 60% of all disaster-related mortality, and have changed the environment dramatically (1). Millions of people are exposed to earthquakes globally because many of the most inhabited cities are built on fault lines. There are several faults in Utah, the longest of which is the Wasatch fault, which runs North-South and is 240 miles in length. Utah's most populous cities are located along this fault, including Salt Lake City, Ogden, and Provo. According to the CDC, a major earthquake affecting a large city has the potential to be the most catastrophic natural disaster for the United States (2). In the weeks following earthquakes, an increase in the number of heart attacks, arrhythmias, increased blood pressure, post-traumatic stress, mental health problems, depression, and suicidal thoughts have been observed and reported (1). Children and the elderly have a higher risk of injury and death during earthquakes than adults. The public health impact of earthquakes is dependent on the magnitude of the earthquake, the nature of the built environment, and the secondary effects of the earthquake such as landslides or fires. The impact may range from deaths and injuries, to secondary infection of untreated wounds, pregnancy complications, increased complications of chronic diseases due to interruption of treatment, and increased psychosocial needs. Environmental consequences often include air, water, and soil pollution. The effects of this kind of pollution can have long-term health effects.

Other Objectives

On average, 800 earthquakes are recorded throughout Utah every year, but only 2% are felt by people. Normally, an earthquake needs to have a magnitude of 3 or greater in order for it to be noticeable by people. An earthquake with a magnitude of 5.5 or higher can cause extensive damage to infrastructure, fires, hazardous materials spills, serious injury, and fatalities. Utah has experienced 16 earthquakes with magnitudes greater than 5.5 since pioneer settlement in 1847. Geologic studies of Utah's faults indicate a long history of repeated large earthquakes of magnitude 6.5 or greater prior to settlement (3). Earthquakes are not predictable and can be devastating, making it very important to for communities and individuals to be prepared. For preparedness information and resources, please visit the [http://www.utah.gov/beready/index.html Be Ready Utah] website.

How Are We Doing?

According to the National Geological Survey, there have been various notable earthquakes reported from 1894 to 1975 throughout Utah (3). Scientists cannot predict when or where the next earthquake will take place.

How Do We Compare With the U.S.?

In the United States, earthquakes are more common on the west coast. However, the damaging effects of an earthquake east of the Rocky Mountains can extend over a much larger area because the eastern half of the country is mainly composed of older rock that has not been fractured and cracked by frequent earthquake activity in the recent geologic past. Rock that is highly fractured and crushed absorbs more seismic energy than rock that is less fractured. Utah and the Intermountain West are seismically active. Utah straddles the Intermountain Seismic Belt's (ISB) Basin and Range Province to the west and Rocky Mountains and Colorado Plateau to the east. The Wasatch fault, where approximately 80% of Utah's population resides, is located within the ISB.

What Is Being Done?

Utah established a working group that has met every year since 2003 to coordinate earthquake research in Utah. This work group reviews research activities, re-evaluates long-term plans for creating earthquake hazard maps, and develops partnerships for investigations on earthquakes. In 2010, the Working Group of Utah Earthquake Probabilities was established to estimate the likelihood of large earthquakes along the Wasatch Front (4). Most casualties and economic losses result from the damage to poorly constructed, older buildings and their unrestrained contents. Improved building codes are now in force statewide, some older buildings have been strengthened, and steps are being taken to upgrade schools and other critical facilities.